Piston



MCL. S. JACKSCN Filed July 17,

@the walls of aucylkinder in whi' Patented 18, 1931)v UNITED STATES PATENTOPFICE WILLIAM MCLEAN STEWART JACKSON, or CLEVELAND,` oHIofAssIGNon. To vTHE GUARDIAN TRUST COMPANY, A CORPORATION OF OHIO PISTON Application led July 17, 1926. Serial No. 123,059.

My invention relates to pistons and relates more particularly to pistons ada table for use in fluid compression pumps, uid Operated brakes, rams, and the like.

An object of my invention is to provide a fpiston wherein little or no leakage of gaseous fluid from the cylinder pressure chamber will occur under widely varying conditions of use to which a piston of this kind may in practice be subjected.A

Another object of-my/invention is to provide a piston of the Huid seal/type wherein wear between *the sealing parts-of the piston and .the cylinder Wall will not be unduly A prevalent.

Another object of my invention is to provide a piston of the gaseous fluid seal typev which will operate without an undue amount of friction to be had between the piston and the cylinder walls, even lunder widely differing operatin` pressure values. K Another object of my invention-is to provide a piston which can be readily, inexpensively manufactured and assembled, and when assembled may be placed in a cylinder of proper bore dimensions and will operate 'efficiently in connection with Vsuch cylinder.

Other objects of my invention and the invention itself will become apparent by reference to the followingdescription of an embodiment of my invention, and which is ilv lustrated in the accompan ing drawings forming apart of this speci cation.

Referringito the drawings:

tional view of an embodiment of my invention, certain portions, however, being shown in elevation therein;

Fig. .2 shows a fragment of the expansion ring element forming( a part of the piston of Fig. 1, the view bein a lan view;

Fig. 3'is a view o a ragment of a pisto and cylinder, mostly in longitudinal medial section, the view being of a modification of the embodimentillustrated in Fig. 1;

Fig. 4 is a like view Of a further imodification; and A Fig. 5 is a lan view of a bearing element. Referring rst to Figs. 1 and 2 at l, I show l1 the piston Fig. L shows "a longitudinal medial sec-v the tubular piston stem 4, a portion 11 of which forms a guiding bearing for the stem 9. A resilient metallic cup 12,seated on the upper surface of the piston disk head 3 isY end 13- of the .stem 4, and is clamped by the nut 10 against the top surfaceof the disk piston head 2, which in turn is clamped against the shoulder 3 of thepiston stem..

A compression spring 14 is compressed between the end wall 16 of the recess 21 in the stem 4, and a washer 20, which is carried by a machine screw 15, is screw threaded into the axialbore of the piston head stem'9.` A metallic expansion ring 17 is placed within the side walls 18 of the cup 12. The upper portions 'of the outer surface of the cup are adapted to contact with the innerwalls of the cylinder 1, the ring 17 being preferably of the form illustrated in Figs. 1 and 2, wherein it is shown to be substantially annular and preferably having one or more diagonal slits 19 at some point in its length. The slit, or slits, should preferably be disposed at an angle of 45 degrees or less, relative to Ca horizontal plane.

When the ring is in place, it communicates a camming effort exerted by the beveled surface 8 of the lpiston head 7, which is seated upon the 'preferably Yrounded inner upper edge of the ring 17, under the influence of the' spring 14, and inaddition to the spring pressure eHect, which constantly tends to expand the c up side walls, this actionA is increased variably according to the variable amount of pressure exerted/by the pressure 05 vcentrally perforated to admit the reduced of gaseous fluid contained `inv the cylinder chamber 22 and which exerts a pressure in the direction of the arrows 23 lupon the entire upper surface of the piston head 7, and which pressure likewise is communicated by the camming action of the beveled surface 8 upon the expansible ring 17 to the cup side walls.

Gaseous fiuid pressure will be communicated, restrictedly, through the slit 19 of the ring 17, between the chamlxer 22 and the space 24 to the rear of the piston head, and I moreover sometimes provide openings-45 through 1 the lateral wall of the ring 17 to increasethe rapidity of equalization of pressures coutained in the spaces 24 and the space between the ring 17 and the cup side walls 18. slit 19 also provides a passage for the4 equalization of pressures in the space 24 and the cylinder chamber 22, whereby gaseous fluid under greater pressure may passv between t-he walls of the slit 19 to the space of less pressure.v These openings are best shown in Fig. 3. l

At 42, 43 and 44, I interpose preferably heat resisting fluid sealing gaskets to prevent the escape of Huid under pressure through the joints containing such gaskets. At 46, the g5 cylindrical exterior surface of the reduced end 13 of the piston stem is carefully machined so as to provide a preferably truly cylindrical guiding surface for the like machined bore surface of the disk 2 which closely fits thereupon. The central cup openlng. has its inner edges closely. engaging this cyhndrical stem surface and is centered thereby. The top surface of the shoulder 3 of the piston stem 4 is carefully machined to form a' planular surface for engagemet with the like planular surface of thc engaging piston head disk 2, so that the disk 2 will be carried in a plane precisely at right angles to the stem axis. The piston disk 2,whichtrans mits the thrust exerted upon the head 7 to the piston stem, has a diameter slightly less than the inside diameter of the cylinder walls, so as to be relieved therefrom, preferably no reliance being placed upon the disk 2 for proper alignment of the piston within the cylinder.`

The piston, upon a pressure stroke responsive to the effect of fluid pressure exerted against its head 7, will move longitudinally under such pressure, and at the same time the space 24 within the cup and to the rear ofthe head 7 will have its gaseous iluid pressure increased by the flow of fluid under pressure from the cylinder .chamber 22 through the slit 19, until, after an interim, the fluid pressure contained in the space to the rear of the head 7, is of such a pressure that upon release of the pressure in the chamber 22, and the out-flow of fluid from the space 24 being 24 over that in the chamber 22will effect a lifting of the piston head 7 fromr its Seat on the ring 17 to permit the ready and quick release of pressure within the space 24, whereby the side walls 18 of the cup will, by their in- The restricted, the excess of pressure in the space- 34 by the automotive brake mechanism or other mechanism actuated by the piston.v

The pressures 45 in the ring 17 increase the rapidity of equalization of pressures on the interior and exterior walls of the ring and may be omitted in most constructions. rIihis operation permits the easy and smooth retraction of the piston after a compression working stroke, and which smooth, easy return is absent in constructions not having this or equivalent pressure relieving means. To further assist in securing a good sea] and a ready release between the contacting portions of the head 7 and the ring 17, I pref` rably round the inner upper edge of the ring which contacts with the beveled edge ofthe head on a radius, and preferably harden the contacting surfaces of the head and the ring so as to increase the longevity of such surfaces and to reduce the frictional resistance exerted between the two surfaces.

The provision of the rounded edge 32 of the ring enables a good seating contact to be had with the beveled edge 8 ofthe hea-d, even though the head is slight-y tilted, and pre` vents a wedging, binding effect which in other constructions might occur.

The contact element 25, screw threaded at 26 into the bore of the tubular stem 4 of the piston body, communicates the 'thrust efforts of the piston to actuate a brake mechanism apparatus. The element 25 has an annular laterally extending flange 26, which oyerlies the end of the stem and a portion 27 of the cylinder end wall to form a stop.

The stem 4 has a pair of oppositely disposed flattened surfaces 59 and 60 relieved from contact with the bearing liner 28, and permits the use of a Wrench engaging lsuch surfaces to prevent rotation of the stem 4 when the contact piece 25 is screw threaded into engagement withfthe threads 6 on the interior of the stem4.

A bearing liner of relatively non-frictional material is shown at 28 between the piston stem and thetubular surface 29 ofthe inner wall of a cylindrical opening passing through when the piston is actuated, and permits also the inflow of air'to the chamber 49 upon a return stroke of the piston. lThe contact piece 25 is adapted to bear at 34 against the mechanism sought to be moved by the piston, such as an automotive vehicle brake mechanism, on.

the like, and which mechanism will preferably resistmovement of the contact piece 25 tlongitudinally of the cylinder and will resiliently exert opposing pressure to the movement of the piston. This opposing .pressure will be eective to restore the piston to its normal position inthe cylinder after the fluid pressure effecting movement of the piston is released.

It is very important that the piston be prevented from cooking, and in the embodiment illustrated, -this is substantially prevented by virtue of the concentricity of the fitting'surfaces of the end plate 33 and the cylinder Wall 1 with the inner wall of the opening through the plate 33 and its boss 27 'Ihev concentricity of the bore 29 in the end cover 33 to the bore of the cylinder 1 is preferably accomplished in the following' manner The end plate 33 ismachined with a reduced section 51, which is concentric with the bushing guide hole 29. This reduced section 51 is made to fit accurately in the cylinder bore and therefore keeps the bore of the bushing 28 concentric with the walls of the cylinder 1. The inner edges of the cylinder wall end are preferably beveled, as shown at 52,

to permit easy insertion of the assembled piston, including the end .wall 33 in the cylinder.

In practice, the side walls of the cup, which are forced into contact with the cylinder side walls in a manne above described, effect an efficient seal against the escape offluid under pressure from the chamber 22 and causes a relatively large surface to contact. with the cylinder sidewalls, whereby the pressure per x unit of contact area is reduced. The cup 18 is relieved from contact with the cylinder walls in its portions r30, which are more nearly adjacent the end wall 12 of ,the cup. i

The distribution of pressure communicated to the side walls ofthe cup 12, effective to'A makeY a seal between the side walls and the cylinder l, maybe varied in different Ways,

and I show, in Fig. 1, a portion 39 of the cup.

adjacent its rim extending beyond the upper edgeV of the ring 17, whic will act as a iexible entering edge upon retractive movements `of the piston and avoids the effect of maxlmum pressure exerted between the outer edge of the cup rim and the cylinder slde Walls.

The reduction of pressure in portions ofthe cup adiacent its rim may also be effected by the expedients illustrated in Figs. 3 and 4, wherein in Fig. 3 the bevel 8 of the head 7 is flattened,rthus reducing the lateral thrust effort of the cam and thus lowering the line of thrust from the ,beveled edge to the cup,

or, asin Fig. 4, by relieving the ring 1 7 in its upper portions, as at 54 and 55. In the embodiment of Fig. 4, `the efect'is much the' same as in the embodiment of Fig.L 1, and the rim of the cup inboth cases is free of the expanding ring. In allvpf the described emfrom that pressure exerted upon'the cylinder side walls by portions of the cup side walls more remote from the rim.

bodiments, the cup rim\ pressure is decreased The cup 18 if of metallic material, and aly o though it may vary in composition, it should7 be of such a material as to have inherentre` siliency and good bearing qualities in its surface portions adapted to contactwith thecylinder walls, and Ihave found that aLspecia-l heat treated alloy of aluminum brone of approximately a composition of 86 per cent copper, 8 per cent zinc, 4 per cent aluminum and 2 per cent iron, is effective to secure very satisfactory resultsunder conditions of use com-A monly encountered. The ring 17 may be made of cast iron or steel, or of a more plastic material so long as a hardened bearing seat 32 is secured. Where the material of the ring is too soft to secure a hardened bearing seat of such material, I contemplate, by fusion or otherwise, securing a bearing seat portion 32 to the body of the ring.` However, I find that a homogeneous ring made from mild steel tubing, so heat treated as to relieve thel inherent strains, operates in a very satisfactory manner for most'purposes.

Where the parts above describedare subjected to rusting conditions, such as in air brake practice, I preferably electrolytically 4 deposit a thin coating ofpcadmium upon such surfaces, excepting that bearing surfaces will not be so coated.v The spring 14 may advantageouslyv vary in strength according to the conditions. of use to which the i but I prefera ly make the spring 14 insufficiently strong to hold the head'? on the seat 32 ,to preveint ready equalization of pressures piston is subjected in practice,

, in the space 24 and the cylinder chamber 22 105 specific embodiment, I am aware that numerous and extensive departures "may be made from the embodiments herein illustrated and described but without departing from the spirit of vmy invention.

I claim:

1. In a piston, the combination with a metallic cup having resilient thin side walls, of a.split metallic ring telescoped within the cup, a piston body carrying said cup, the cup Vside vwalls being projected forwardly there- .from,ofa piston' headnormally-.spring pressed toward the piston body and making at an edge portion engagement with an inner upper portion of the ring, said head movable under,

the combined effects of spring pressure and pressure of fluid exerted against its outer surace to cam the ring outwardly toelfect expansion of portions of cup side Walls adjacent its rim into sealing engagement with enclosing cylinder walls.

2. In a piston, the combination with a metallic cup having a relatively thin side wall, of asplit metallic ring telescoped within the cup, a piston body carrying said cup with its side walls projecting forwardly therefrom, of a piston head normally spring pressed t0- ward the piston body and making at an edge portion a camming enga-gement with an inner upper edge of the said ring to expand the ring against the inner side walls of the cup, saidvhead adapted to present a pressure face to the pressure of fluid which may be contained under pressure in a cylinder in which the piston may be placed, said head movable under the combined effects of spring and fluid pressures'to cam the ring outwardly to expand portions of the cup side walls adjacent its rim into effective sealing engagement with the walls of such cylinder.

3. In a piston, the combination with a resilient cup, of a split metallic ring telescoped within the cup, a piston body carrying said cup with its side walls projecting forwardly therefrom, of a piston head normally spring pressed toward' the piston body and making at an edge portion a camming engagement with an inner upper portion of the said ring to expand the ring against the inner side walls of the cup, said head adapted to p resent a pressure face to the pressure of fluid which may be contained under pressure in a cylinder in which the piston may be placed, a spring, said head movable under the effect of pressure exerted by the spring to cam the ring outwardly to expand the portions of the i cup side walls adjacent Lits rim into effective seahng engagement with the walls of such cylinder, said ring having a wall thickness adjacent the line of contact between the head and the ring at least three vtimes the thickness of the adjacent cup side wall portion.

4. In a piston, the combination with ametallic cup havin a relatively thin side wall of a split metallic ring having a cylindrical outer face .telescoped within the cup, a piston body carrying said cup with its side walls projecting forwardly therefrom, of a piston head normally spring pressed toward the piston body and making at an edge portion a camming engagement with an inner upper portion of the said ring to expand the ring against the inner side walls of the cup, said head adapted to present a pressure face to the pressure of uid which may be contained under pressure in a cylinder in which the piston may be placed, said head movable under thfeeffect of such uid pressure to cam the ring outwardly to expand the portions of the cup side walls adjacent its rim into effective sealin engagement with the walls of such cylin er, said ring contacting with the side walls of the cup along the upper inner'surface of such side walls and being ret0 expand the ring against the inner side walls 0f the cup, said head adapted to present a pressure face'to the pressure of fluid which may be contained under pressure in a cylinder in which the piston may be placed, said head movable under the combined effects of spring and fluid pressures to cam the ring outwardly to expand the portions ofthe cup side walls adjacent its rim into pressure s'ealing engagement-with the Walls of such cyl-- inder, said rin having a wall thickness'adjacent theline o contact between the head and the ring at least three times the thickness of the adjacent cup side wall portion, and being of reduced wall thickness and disposed out of engagement with the cup side walllpor tions adjacent the cup end wall.

6. In a piston, the combination with a metallic cup having a relatively thin side wall, of an expansible resilient metallic ring telescoped within the cup, a piston body carrying said cup with its side walls projecting forwardly therefrom, of a piston head normally spring pressed toward the piston body and making at an edge portion Ia camming ensaid ring to expand the ring a ainst the inner side walls of the cu said ead adapted to present a pressure ace to the pressure of fluid which may be contained under pres'- sure in a cylinder in which the piston may be placed, of said head movable under the combined efects of sprin j and fluid pressures to cam the ring outwardly to expand the portions of the cup side walls adjacent its rim into pressed sealin engagement with the walls of suchscylin er, said cup being of a relatively more resilient material than the material of said ring.

7. In a piston, the combination with a metallic cup having resilient thin side walls, of

Aan expansible metallic ring telescoped within the cup, a piston body carrying said cup, the cup side walls being projected forwardly therefrom, of a piston head normally spring engagement with enclosing cylinder walls.

8. In a piston, the combination with a me- 'tallic cup having resilient thin side walls, of

an expansible metallic ring telescoped within the cup, a piston body carrying said cup, the

cup side walls being projected forwardly therefrom, of a piston head normally spring pressed toward the piston body and making, at an annular portion, engagement with an inner upper portion of the ring, said head movable under the combined effects of spring pressure and pressure of fluid exerted against its outer surface to cam the ring outwardly to effect expansion of portions of the cup side walls into sealing engagement with enclosing cylinder Walls, the cup being relieved from the cylinder side walls in portions adjacent its end Wall, the ring being'likewise relieved from such cup side wall portions.

9. In a piston, the combination with a metallic cup having resilient thin side walls, of an expansible metallic ring telescoped within `the cup, a piston body carrying saidv cup, the cup side walls being projected forwardly therefrom, of a piston head normally spring pressed toward the piston body and making, at an annular portion, engagement with an inner upper portion of the ring, said lhead movable' under the combined effects of enclosing cylinder walls, the ring making enspring pressure and pressure of Huid exerted against itsouter surface to cam the ring outwardly to effect expansion of portions of the cup side walls into sealing engagement. with gagement with the piston along an inner up- .per edge, which is convexly rounded transversely.

l 10. In a piston, the combination with a piston stem having an axial bore, one. endA of the vstein being reduced and exteriorly threaded, a head disk having a central cylindrical aperture tted over the reduced end of the stem and seated on the shoulder adjoining such reduced end, a ,metallic cup having resilient side walls seated on the disk with its side walls extending therefrom, saidcuphaving its end walls icentrallV apertured and passedv over the reduced en of the stem, a

- clamping nut screw threaded onto the` exteriorly threaded, portion of the stem tov clamp the cup and head disk against said shoulder,- a movable piston head oflpoppetl N an axial stem projected within the bore of the `stemreduced portion valve form having and guided by the inner walls thereof, an expansible split .ring 17` disposed within the side walls of the cup and expandible by the efect of the movement of the head toward j the said head disk, avspring disposed within the stem bore engaging the movable head and exerting a constant pressuretending to move the head toward said head disk, said head being responsive to fluid pressure on its outer surface to cause an increase in pressure tending to expand the ring.

11. In an air brake operating cylinder, the 70 -adjacent the cup end wall, -a piston head havmg an axial stemprojected through the pis- -ton stem and guided thereby and a flanged head engageable at a beveled portion with the rounded edge of the ring, spring means for resiliently effecting a constant pressure on the piston head to expand the ring against the inner walls -of the cup, said spring pressure being of suilicient' ma 'tude as to effect expansion of the cup side walls against the,cylinder walls into effective sealing engagement with the cylinder walls.

12, In an air brake operating cylinder, the combination with a cylinder and a piston reciprocable therein, the piston comprising a y metallic cup having flexible side walls, a disk, said cup mounted upon said Ydisk and a stem with a reduced'cylindrical'upper portion on which said disk and said cup is concentrically mounted, means cooperating with the end of the reduced portion lwithin the cup to eiect a clamping of the inner portions of the cup and disk on the stem, a dia onallyv split metal ring telescoped Lwithin e cup rin havinganinner `upperdrounded edge an an outer wall reduced in its portion adjacent the cup end wall, a piston head having an axial stem projected through the piston stem and guided thereby, and a flanged head engageable at a beveled portion with the rounded edge of the ring, spring means for resiliently effecting -a constant pressure on the piston headvto, expand the ring against the inner wallsofthe cupi ySaid spring pres 4sure being ofsugcientmagnitude as to efs feet expansion'ofthe cup side walls` against wiLuAu lema mmm' Jackson. 

